首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
The putP gene encodes the major proline permease in Salmonella typhimurium that couples transport of proline to the sodium electrochemical gradient. To identify residues involved in the cation binding site, we have isolated putP mutants that confer resistance to lithium during growth on proline. Wild-type S. typhimurium can grow well on proline as the sole carbon source in media supplemented with NaCl, but grows poorly when LiCl is substituted for NaCl. In contrast to the growth phenotype, proline permease is capable of transporting proline via Na+/proline or Li+/proline symport. Therefore, we selected mutants that grow well on media containing proline as the sole carbon source in the presence of lithium ions. All of the mutants assayed exhibit decreased rates of Li+/proline and Na+/proline cotransport relative to wild type. The location of each mutation was determined by deletion mapping: the mutations cluster in two small deletion intervals at the 5' and 3' termini of the putP gene. The map positions of these lithium resistance mutations are different from the locations of the previously isolated substrate specificity mutations. These results suggest that Lir mutations may define domains of the protein that fold to form the cation binding site of proline permease.  相似文献   

2.
The regulation of phs [production of hydrogen sulphide (H2S)] in Salmonella typhimurium is complex. Previous studies have shown that expression is dependent upon the presence of reduced sulphur and anaerobiosis and is modulated by carbon source and growth stage. Transposon mutagenesis failed to find any potential trans-acting factors effective in the regulation of phs in relation to oxygen. Spontaneous mutants capable of expressing phs-lac aerobically were isolated and characterized. These mutations are closely linked to phs and affect not only oxygen regulation but also the requirement for cyclic AMP and reduced sulphur. Analysis of merodiploid strains indicates that these mutations cis-acting and that phs is not subject to autoregulation.  相似文献   

3.
The gene encoding nucleosidediphosphate kinase (ndk) was located at 55 units on the Salmonella typhimurium chromosome. The ndk locus was 83% cotransducible with hisS and 2% cotransducible with glyA in phage P22-mediated crosses. A nucleosidediphosphate kinase mutant that produced only 10% of the wild-type enzyme activity (ndk-1) grew normally and produced a heat-labile enzyme.  相似文献   

4.
5.
A mutator mutation of Salmonella typhimurium, observed in a strain resistant to P22 and rifampin, affects mutation rates of bacterial, R factor, and prophage P22 genes.  相似文献   

6.
When R factor 222 is transduced by bacteriophage P22 in Salmonella typhimurium, most recipient bacteria which adsorb transducing particles do not give rise to transductant clones (i.e., transduction is abortive); however the transduced drug-resistance genes can be rescued by recombination with the resistance-transfer factor or R factor carried by the recipient.  相似文献   

7.
8.
In order to elucidate the biosynthesis of the base moiety of cobalamin in Salmonella typhimurium LT2, this organism was grown in the presence of [1′-14C]riboflavin. The vitamin B12 isolated was 14C-labeled. It was shown by chemical degradation that the 14C-label was exclusively localized in carbon atom 2 of the 5,6-dimethylbenzimidazole moiety. This demonstrated the precursor function of riboflavin in the biosynthesis of 5,6-dimethylbenzimidazole in S. typhimurium. Received: 25 August 1998 / Accepted: 27 October 1998  相似文献   

9.
10.
The role of a stress-response protein in Salmonella typhimurium virulence   总被引:35,自引:0,他引:35  
We recently described the use of selective transposon mutagenesis to generate a series of avirulent mutants of a pathogenic strain of Salmonella typhimurium. Cloning and sequencing of the insertion sites from two of these mutants reveals that both have identical locations within an open reading frame that is highly homologous to a gene, htrA, encoding a heat-shock protein in Escherichia coli. DNA sequence analysis of S. typhimurium htrA reveals the presence of a gene capable of encoding a protein with a calculated Mr of 49316 that has 88.7% protein:protein homology with its E. coli counterpart. In E. coli, lesions in this gene, also known as degP, reduce proteolytic degradation of aberrant periplasmic proteins. Characteristics of the S. typhimurium htrA mutants, 046 and 014, in vivo and in vitro suggested that they are avirulent because of impaired ability to survive and/or replicate in host tissues. In vitro, the S. typhimurium htrA mutants 046 and 014 are not temperature-sensitive but were found to be more susceptible to oxidative stress than the parent, suggesting that they may be less able to withstand oxidative killing within macrophages.  相似文献   

11.
The plasmid of Salmonella typhimurium LT2   总被引:18,自引:0,他引:18  
Summary Methods of clonal analysis were applied to the study of heterogeneity of the progeny after crosses of 4 donor strains (Hfr H, Hfr C, KL 16 and KL 99) with 3 recipient strains (PC 0212, AB 712 and ECK 022). Three markers were used in each cross. The distal one was the selective marker. The inheritance of two additional proximal markers characterized the heterogeneity of clones originating from particular zygotes. In most crosses the percentage of heterogeneity exceeded 30. One of the recipient strains, obtained by conjugation of the conventional strain PC 0212 with the donor Hfr H revealed unusual properties in respect to heterogeneity. Exconjugants derived from this recipient (ECK 022) and donor Hfr H and Hfr C had a heterogeneity index of about 5%. It is shown that this unusual behavior reflects a very fast process of segregation of recombinants.In crosses with the donors KL 16 and KL 99 the same recipient revealed normal indices of heterogeneity. All these data are explained assuming that there exists a specific genetic marker which determines the process of decay of merozygotes. Tentatively it is called het. Its approximate localization was deduced from specifically designed experiments, in which the heterogeneity of the progeny was found very different, when the donor KL 16 transmitted different parts of its chromosome to the recipient ECK 022.  相似文献   

12.
13.
Twelve bacteriphages lysing only smooth Salmonella typhimurium strains were shown to have similar morphology--an icosahedric head to which a short, noncontractile tail carrying six spikes was attached. All phages degraded their lipopolysaccharide (LPS) receptors as shown by their ability to cleave off [14C]galactosyl-containing oligosaccharides from S. typhimurium cells labeled in their LPS. The oligosaccharides inhibited the alpha-D-galactosyl-specific Bandeiraea simplicifolia lectin agglutination of human type B erythrocytes, indicating that all 12 phage glycanases were of endorhamnosidase specificity, i.e., hydrolyzed the alpha-L-rhamnopyranosyl-(1 leads to 3)-D-galactopyranosyl linkage in the S. typhimurium O-polysaccharide chain. Two of the phages, 28B and 36, were studied in more detail. Whereas the phage 28B glycanase hydrolyzed the S. typhimurium LPS into dodeca- and octasaccharides, the phage 36 glycanase in addition cleaved off tetrasaccharides. Both phage enzymes hydrolyzed the O-polysaccharide chains of LPS from Salmonella belonging to serogroups A, B, and D1, which are built up of tetrasaccharide-repeating units identical except for the nature of the 3,6-dideoxyhexopyranosyl group (R). : FORMULA:(SEE TEXT). The phage 28B and 36 endorhamnosidases hydrolyzed also an LPS from which the 3,6-dideoxyhexosyl substituents had previously been hydrolyzed off. However, neither of the enzymes was active on LPS preparations in which the C2-C3 bond of the L-rhamnopyranosyl ring had been opened by periodate oxidation. Glucosylation at O-6 of the D-galactopyranosyl residues in the S. typhimurium LPS was found to be incompatible with hydrolysis by both enzymes. However, in an LPS glucosylated at O-4 of the D-galactopyranosyl residues, the adjacent alpha-L-rhamnopyranosyl linkages were found to be perferentially cleaved.  相似文献   

14.
15.
16.
17.
The 1-nitropyrene reductase of Salmonella typhimurium   总被引:1,自引:0,他引:1  
We have devised a sensitive fluorimetric assay to monitor the conversion of 1-nitropyrene to 1-aminopyrene. Application of this assay to extracts of Salmonella typhimurium strains TA98 and TA100 (which are sensitive to the mutagenic and lethal effects of 1-nitropyrene) has shown that these bacteria contain 'nitropyrene reductase' activity at the low level of 10(-11) mol/min/mg protein. NADPH and NADH serve equally well as reducing agents. The nitropyrene reductase activity of strain TA100 F50 (a mutant resistant to 1-nitropyrene) was found to be considerably lower.  相似文献   

18.
The kinetic mechanism of the CheR methyltransferase, S-adenosyl-L-methionine (AdoMet): protein-L-glutamate O-methyltransferase (EC 2.1.1.24), from Salmonella typhimurium was investigated. Initial velocity, product inhibition, and binding studies were performed, and from the data obtained, it was determined that the mechanism of the reaction catalyzed by the enzyme is random. Initial velocity rates were measured with varied amounts of both substrates, and double-reciprocal plots gave patterns which converged on or near the abscissa. The products, S-adenosyl-L-homocysteine and methylated receptor, were found to be competitive inhibitors with respect to both AdoMet and receptor. Equilibrium dialysis and immunoprecipitation studies indicated that the two substrates can bind to the enzyme independent of each other. These results are consistent with a random mechanism with no abortive complexes being formed. The Michaelis constants calculated for AdoMet and receptor were 8.62 microM and 2.03 mg/ml total membrane protein (approximately 2.10 microM Tar protein), and the apparent dissociation constants of AdoMet and the receptor were 16.8 microM and 4.07 mg/ml total membrane protein (approximately 4.2 microM Tar protein), respectively. The Kd of AdoMet for the enzyme was 10.9 microM as determined by binding studies.  相似文献   

19.
20.
Thirteen conditional lethal mutations in genes of Salmonella typhimurium map at the clmF locus and affect both viability and the faithful partitioning of daughter nucleoids. These mutations have now been divided into three complementation groups by using cloned fragments of S. typhimurium DNA and renamed parC, parE, and parF. The proteins produced from the cloned fragments predict that ParC is an 85-kD protein, ParE is 75 kD in size, and ParF, 27 kD. The parE gene is about 5 kb upstream of the parC gene, and parC is just upstream of parF. Genes situated between parC and parE produce at least two proteins of unknown function. The DNA sequence of the S. typhimurium parC gene was determined and has 56% homology with the first 1400 base pairs of the Escherichia coli gryA gene, which encodes the A subunit of DNA gyrase, and 85% homology with the E. coli parC gene. Despite the strong homology between gryA and parC, these two genes cannot substitute for one another. The DNA sequence of the S. typhimurium parF gene was determined and predicts a protein with a hydrophobic N terminus. The ParF protein may interact with ParC and ParE to anchor these proteins to the membrane. These results raise questions about the relative roles of gyrase and ParCEF in nucleoid decatenation. In addition, the parC and gyrA genes provide an example of the evolution of essential functions by gene duplication.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号